In a motor vehicle with a classic onboard power supply system, only one battery is typically available, which battery can be embodied, in particular, in the form of a known car battery, that it to say a rechargeable battery. This battery typically supplies energy to all loads, including the starter, if a generator does not deliver any energy. In the case of a running internal combustion engine, however, typically two redundant electrical energy sources are available, namely the battery and also a generator driven by the internal combustion engine. If one of the energy sources fails, the respectively other source can thus continue to supply power to the onboard power supply system.
In recent years, automatic stop-start systems, which switch off the internal combustion engine in the case of very low speeds of the motor vehicle, have been built into motor vehicles for reasons of consumption minimization. As a result thereof, the generator is omitted in the case of a switched-off internal combustion engine as the second, redundant current source. However, should the battery fail at the same time, a safe restart of the internal combustion engine would not be possible. This failure can also endanger, in particular, the safety of the vehicle, the vehicle occupants and further road users, for example when the vehicle has come to a standstill at a railroad crossing.
In order to minimize the risk of a battery failure, motor vehicles with stop-start systems are usually equipped with battery sensors, in particular intelligent battery sensors, which make it possible to monitor the battery and hence the ability of the motor vehicle to start. Should a weak battery be identified, the internal combustion engine is not deactivated. Possible causes for a sudden failure of the battery can be, for example, a break in the intercell connector (electrical connection between two cells of the battery), a drop in the positive or the negative pole terminal of the battery poles (in the case of insufficient press-contact), or melting through of the pole shank (between the pole and the first/last cell) due to thermal overloading.